Cryopreservation prevents arterial allograft dilation

Historically, immune-mediated degradation and subsequent aneurysm formation have limited the usefulness of cryopreserved arterial allografts. This study tested the hypothesis that modern cryopreserved arterial allografts are protected from immune-mediated dilation. Abdominal aortas were harvested from anesthetized rats (Lewis and Brown-Norway) for immediate implantation or cryopreservation. Subsequently, Lewis rats underwent infrarenal aortic replacement with either an acutely harvested or a cryopreserved graft. There were four experimental groups: (1) acutely harvested isografts (Iso; n = 6), (2) cryopreserved isografts (C-Iso; n = 6), (3) cryopreserved allografts (C-Allo; n = 6), and (4) acutely harvested allografts (Allo; n = 6). All grafts were explanted at 8 weeks. A video camera and edge detection software were used to measure systolic and diastolic in vivo graft diameter (d). Measurement of arterial blood pressure (p) allowed calculation of compliance (Dd/Dp). Tail-cuff plethysmography was used to assess graft patency at 1 week. Graft diameter and blood pressure measurements were repeated at harvest. All harvested grafts were examined histologically. Our results showed that cryopreservation prevented immune-mediated dilation in arterial allografts in our 8-week rat implant model. Furthermore, the compliance of the cryopreserved grafts and was similar to that of controls. Further investigation is needed to delineate the exact mechanism of these potential clinically significant findings.

The mechanical properties of fresh and cryopreserved arterial homografts

OBJECTIVES

To assess the effect of cryopreservation on the elasticity and compliance of arterial allografts.

MATERIALS AND METHODS

Iliofemoral segments of arteries and veins harvested from multiorgan donors were divided into two groups: fresh-control, tested for 24 hours after harvesting, and cryopreserved in liquid nitrogen after pretreatment with 20% dimethylsulphoxide and stored for an average time of 22 days. Vessel wall elastic properties were evaluated from the stress-strain relationship in a specially designed test cell fixed to the Instron Universal Testing Machine.

RESULTS

The elastic modulus of the artery control group (1.54+/-0.33 MPa, n=20) was not significantly different from the cryopreserved group (1.69+/-0.61 MPa, n=15). Similarly, values for unfrozen veins (3.11+/-0.65 MPa, n=47) were not significantly different from those of frozen samples (2.71+/-0.85 MPa, n=38). Control compliance (6. 86+/-1.79x10(-5)%/Pa, for arteries; 3.84+/-0.81x10(-5)%/Pa, for veins) was similar to that of the cryopreserved group (6.66+/-1. 80x10(-5)%/Pa, for arteries; 4.16+/-1.21x10(-5)%/Pa, for veins).

CONCLUSIONS

Cryopreservation maintains the important elastic properties of arterial and venous allografts during average storage time of 22 days.

Changes in the cooling rate and medium improve the vascular function in cryopreserved porcine femoral arteries

PURPOSE

The purpose of this study was to design an adequate technique with which to cryopreserve pig femoral arteries and to assess the influence of storage times in vascular function.

METHODS

Fifty-two femoral arteries were distributed in seven groups. In group A (control), 10 arteries were studied after harvest; in groups B1 and B2, 19 arteries were suspended in RPMI 1640 plus fetal calf serum plus dimethylsulfoxide and were cryopreserved at 1 degrees C per minute or 0.3 degrees C per minute, respectively. In groups C1 to C4, 23 arteries were suspended in modified Krebs-Henseleit plus dimethylsulfoxide plus sucrose, cryopreserved at 0.7 degrees C per minute, and kept frozen for 1, 15, 60, or 180 days, respectively. After being thawed, arteries were examined for contraction and endothelial-dependent vasodilation (organ bath studies), antithrombotic properties of the endothelial layer(perfusion studies), and vessel structure (electron microscopy).

RESULTS

Endothelial cells were present in both cryopreserved and control arteries. The control vessels showed a mean contraction to norepinephrine (10(-7) mol/L) of 13010 +/- 3181 mg. Arteries in groups B1 and B2 did not respond to norepinephrine. Contraction in groups C1 to C4 was as follows: C1, 5354 +/- 1222 mg; C2, 5187 +/- 2672 mg; C3, 6867 +/- 2292 mg; C4, 7000 +/- 2858 mg, which represent 50% of the control values (P <.001). Vasodilation was similar in control (99% +/- 3%) and cryopreserved arteries (C1, 90% +/- 13%; C2, 93% +/- 12%; C3, 89% +/- 15%; C4, 88% +/- 22%). Storage time did not influence vascular function. Platelet interaction was almost absent and similar in all groups.

CONCLUSION

A modified cryopreservation technique preserves endothelial function independently of the storage time up to 6 months.

Effects of cryopreservation on contractile properties of porcine isolated aortic valve leaflets and aortic wall

Human semilunar donor heart valves can be stored in banks, awaiting transplantation. To evaluate the result of the preservation protocols, a quantitative description of the tissue is necessary. In this study we investigated in a quantitative way the contractile properties of fresh and cryopreserved porcine isolated aortic heart valve leaflets in response to a number of endogenous vasoactive compounds. The responses of strips of the aortic wall were included for comparison. Contraction was measured isometrically in response to potassium (K+; 100 mmol/L), 5-hydroxytryptamine (1 nmol/L to 100 micromol/L), noradrenaline (1 nmol/L to 100 micromol/L), endothelin-1 (0.01 nmol/L to 0.3 micromol/L), and prostaglandin F(2alpha) (0.1 nmol/L to 10 micromol/L). The pharmacologic parameters E(MAX) (the maximal response expressed as a percentage of contraction to a 100 mmol/L dose of K+) and EC50 (the concentration that produces 50% of the maximal effect) were calculated for every compound (n = 6 to 7 each). We observed that all specimens contracted in response to potassium. Its magnitude in fresh leaflets equaled 1.6 +/- 0.14 mN compared with 26.6 +/- 2.6 mN in fresh aortic wall. Noradrenaline, endothelin-1, and prostaglandin F(2alpha) all caused contraction in valvular leaflets and aortic wall, whereas 5-hydroxytryptamine caused contraction in the valvular leaflets but relaxation in aortic wall. After cryopreservation, the response to K+ amounted to 24% of the response of the fresh specimens in valvular leaflets (n = 25) and 14% in aortic wall (n = 26). The values of E(MAX) and EC50 of the responses to noradrenaline, endothelin-1, and prostaglandin F(2alpha) remained unchanged. Although the physiologic relevance of contraction of valvular leaflets needs further study, its measurement may provide an additional model to verify the consequences of alternative methods of preservation.